Cancelled PS CS6 subscription copy won't let me enter my retail serial number

Question

I bought a Photoshop CS6 subscription a week ago, then decided I'd rather have the retail version. I have the appropriate retail copy, with a serial number in the box.
I called Adobe to cancel my subscription, and it's marked as cancelled now, though the cancellation email says I can continue using the subscription until next month.
I deactivated Photoshop, expecting that I'd then be able to enter my retail serial number, but when I try to license it, it doesn't even let me enter a serial number - it just detects the (just cancelled today, but still active) subscription and says thanks very much.
I'd like to enter my retail serial number without waiting a month for the cancelled subscription to fully go away.
I appreciate that this isn't exactly a terrible problem to have, and it's not a big deal. But is there any way to force it to let me enter my serial number, even though the subscription is still active? I'd prefer to avoid uninstalling the downloaded subscription copy, and reinstalling from the (ugh) DVD in the retail box - especially if that one will just pick up the subscription too!

Answer 1

I found the answer myself:
1. Deactivate Photoshop (via its Help menu) over the internet.
2. Quit and relaunch Photoshop. It will now think it's the Photoshop Extended Trial version, and it'll ask to register the trial with your Adobe account. Don't do that.
3. Quit and relaunch Photoshop again. It will say you have 30 days left in your trial, and you can either click the "License" button or "Continue Trial". First, disconnect from the internet (switch off your computer's wifi, or such - make sure there's no internet connection).
4. Click "License". It will fail to connect to Adobe, and will then give you an "Enter Serial Number" option.
5. Enter your serial number, reconnect to the internet, and submit the serial number. Let it register the serial number to your Adobe Account online.
6. Quit and relaunch Photoshop one more time, and you're done. Your Adobe Account online will show your new Photoshop serial number as registered.
Whew. But at least there was no need to wait a month, or to uninstall/reinstall.